Optical networks are evolving towards a mesh architecture. In optical mesh networks, the network topology consists of nodes and interconnecting links. The traffic on the fiber-optic links utilizes wavelength-division multiplexing (WDM) for increasing the capacity on the link. At the network nodes, the channels on ingress fibers are either routed to egress fibers for transmission to subsequent network nodes, or the channels terminate at the node for local utilization of the information carried therein. The hardware to implement this functionality at the node can be based on electronic switching fabrics, requiring optical-to-electronic-to-optical conversions, or they can be implemented entirely in the optical regime. The latter approach is advantageous due to savings in cost, power consumption, and space requirements.
FIG. 1 depicts a conventional network node architecture 100 An ingress fiber 102 (out of multiple ingress fibers, rest not shown) connects to an input port 106 of a demultiplexing-type wavelength-selective switch (WSS) 110. Other multiple ingress fibers of the node (not shown in FIG. 1) are each connected to an input port of other demultiplexing-type WSS's (also not shown). WSS 110 has a single input port 106 and multiple output ports 114-A through 114-D. WSS 110 can route the WDM channels in an independent and reconfigurable fashion from input port 106 to any one of output ports 114-A through 114-D. In the network node architecture illustrated in FIG. 1, channels that are destined from ingress fiber 102 to continue to an egress fiber 126 are routed by WSS 110 to output port 114-C. Output port 114-C is connected to an input port 116-C of a multiplexing-type WSS 120. WSS 120 has multiple input ports 116-A through 116-D and a single output port 122. WSS 120 can route any WDM channel in an independent and reconfigurable fashion from any one of input ports 116-A through 116-D to output port 122. Therefore, channels that are destined from ingress fiber 102 to continue to egress fiber 126 are routed by WSS 110 to output port 114-C and further routed by WSS 120 to output port 122, which is connected to egress fiber 126. The network node shown in FIG. 1 would typically have additional egress fibers, which are not shown here. Other multiple egress fibers of the node (not shown in FIG. 1) are each typically connected to the output of other multiplexing-type WSS's (also not shown). Output ports 114-A and 114-B of WSS 110 are each connected to one input port of such other WSS for routing channels from ingress fiber 102 to other egress fibers. Channels that are destined from ingress fiber 102 to be utilized locally at the node are routed by WSS 110 to output port 114-D, which is connected to the input of a demultiplexer 130. Demultiplexer 130 passively separates the WDM channels to output ports 134-A through 134-N, where the separated channels can be detected by opto-electronic means. In an analogous manner, channels that are added at this network node for transmission to egress fiber 126 are connected to ports 136-A through 136-N of multiplexer 140, and an output 142 of multiplexer 140 is connected to input port 115-D of multiplexing-type WSS 120. WSS 120 routes the added channels from input port 116-D to output 122, which is connected to egress fiber 126.
What is needed are methods and apparatus for reducing the number of individual components, and reducing the losses conventionally incurred in routing optical signals from an ingress fiber to drop ports, and in routing optical signals from add ports to an egress fiber.